The present invention concerns the manufacture of tires. More particularly, it relates to the process of molding tire treads, molds used in the process of molding tire treads, and tires produced using such molds.
U.S. Pat. No. 5,492,669 and EP 0 569 909 describe a type of mold in which a very large number of molding elements, in the form of sheets that are arranged transversely. The molding surface consists of the juxtaposed group of borders or edges of each sheet. Because the sheets are orientated transversely, they extend from one shoulder of the tire to the other. U.S. Pat. No. 5,980,810 and EP 0 860 260 propose to maintain the orientation of the sheets as perfectly radially as possible through the use of intermediate sheets, which are themselves engaged in slits machined into a supporting ring, and which are therefore guided rigorously.
Particularly with certain types of tread pattern, the venting of such molds can prove to be locally inadequate. The sheets of the mold can gradually become clogged as more and more tire fabrication cycles are carried out. This progressively reduces the venting ability of the mold, making it necessary to clean the mold regularly in order to guarantee the quality of the appearance of the tires produced.
Furthermore, the opening and closing of molds of this type requires coordinated movement in a radial direction, of all the sheets which, together, form a laminated peripheral crown. Parasitic frictional effects can oppose the opening and closing movements of the mold. In addition, it can prove difficult to maintain a regular distribution of the clearances between sheets. Consequently, molding burrs can appear in places where the clearance between sheets has become larger than the nominal clearance. One objective is to choose the nominal clearance, as explained in patent U.S. Pat. No. 5,492,669, specifically to prevent the rubber from flowing between the sheets at any time during the closure of the mold.